Abstract
Opiates function as immunomodulators, partly by their effects on T cells. Opioids act via μ-, δ-, and κ-opioid receptors, among which the μ-type is of particular interest, because morphine-like opioids preferentially bind to it. Here we report that μ-opioid receptor mRNA was induced after CD3/28-mediated activation of primary human T lymphocytes and Jurkat T cells, neither of which expresses the gene constitutively. Moreover, a reporter gene construct containing 2624 base pairs of the μ-opioid receptor promoter was transactivated by CD3/28 stimulation. Transcriptional induction of the μ-opioid receptor gene was mediated by activator protein-1 (AP-1), nuclear factor-κB, and nuclear factor of activated T cells (NFAT). NFAT was found to bind to three sequences of the μ-opioid receptor promoter, located at nucleotides -1064, -785, and -486. Although the -486 element is in close proximity to a putative AP-1 site, there was no evidence for a combined AP-1/NFAT site. Furthermore, we demonstrated that the induction of inter-leukin-2 mRNA and protein in activated T cells was inhibited by morphine in cells, in which μ-opioid receptors had been induced by CD3/28 monoclonal antibodies (mAbs), and that this effect was blocked by the μ-opioid receptor-specific antagonist d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH2. CD3/28 mAb-induced interleukin-2 transcription was also inhibited by the opioids fentanyl and loperamide. This indicates that the induced μ-opioid receptor mRNA is translated into functional receptor protein. Furthermore, a μ-opioid receptor-enhanced green fluorescent protein-fusion protein was localized in membranes of Jurkat cells and internalized in response to [d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin but not morphine. In conclusion, these data emphasize the role of opioids in the modulation of T lymphocyte signaling.
Footnotes
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This work was supported by a research grant of the government of the state of Sachsen-Anhalt (N2/ND: Physiologie und Pathophysiologie signalüber-tragender Netzwerke im Immun- und Nervensystem) (to V.H. and B.S.) and a grant from the Deutsche Forschungsgemeinschaft (KR 1740/10-1) (to J.K.).
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ABBREVIATIONS: IFN, interferon; AP-1, activator protein-1; CTAP, d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH2; DAMGO, [d-Ala2,N-MePhe4,Gly5-ol]-enkephalin; IL, interleukin; mAb, monoclonal antibody; NFAT, nuclear factor of activated T cells; NF-κB, nuclear factor κB; nt, nucleotide; RT-PCR, reverse transcription-polymerase chain reaction; STAT, signal transducer and activator of transcription; TNF, tumor necrosis factor; tk, thymidine kinase; EMSA, electrophoretic mobility shift assay; ELISA, enzyme-linked immunosorbent assay; CAT, chloramphenicol acetyltransferase; MOR, μ-opioid receptor; mu, mutated.
- Received February 4, 2008.
- Accepted May 7, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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